On the detection of shunts in silicon solar cells by photo‐ and electroluminescence imaging

Abstract

Recently electroluminescence (EL) and photoluminescence (PL) imaging were reported to allow detection of strong ohmic shunts in silicon solar cells. Comparing lock-in thermography (LIT) images with luminescence images of various shunted cells, measured under different conditions, the ability of luminescence techniques for shunt detection is investigated. Luminescence imaging allows identifying ohmic shunts only if they reach a certain strength. The detection limit for PL measurements of linear shunts was estimated to be in the order of 15 mA at 0Á5 V bias for a point-like shunt in multicrystalline ( Electro-and photoluminescence (EL and PL) imaging have been introduced as very efficient techniques for spatially resolved characterization of silicon solar cells.1,2 Specifically the localization of strong ohmic shunts in industrial multicrystalline (mc) silicon cells via EL and PL imaging has recently been reported. 3,4,5,6 However, besides ohmic shunts, there are also other types of shunts, like non-linear shunts and prebreakdown sites.7 While ohmic shunts show a linear current-voltage (I-V) characteristic and usually also dominate under high reverse bias, the I-V characteristic of non-linear shunts is diode-like, with the higher conductivity in silicon cells always in forward bias direction. Non-linear shunts can be caused by strongly recombination-active defects crossing the pn-junction or by a direct contact of the grid metal to the base (Schottky-type shunts). These non-linear shunts are generally less harmful than ohmic shunts, but they also degrade the fill factor and the low light level performance of solar cells.8 Pre-breakdown sites show no or only a weak conductivity under low forward and reverse bias, but a strongly increasing conductivity for higher reverse bias above À5 V typically. They are avalanche breakdown sites, caused by defects crossing the pn-junction or other reasons of local high fields. If these pre-breakdown sites show currents of several amperes at reverse voltage of À13

Defect induced non-ideal dark – characteristics of solar cells

“…This light emission is a standard failure analysis technique for integrated circuits. It has also been observed for monocrystalline silicon solar cells [19]. The general explanation of light emission under high field conditions is bremsstrahlung, which is light emission due to acceleration or deceleration of carriers.…”

Luminescence emission from forward- and reverse-biased multicrystalline silicon solar cells

“…Thus, prebreakdown sites under reverse bias can be well characterized by dark lock-in thermography ͑reverse-DLIT͒. 54 However, the high spatial resolution of the luminescence images showing breakdown sites with diameters of some 10 m is masked in the DLIT measurements by the heat distribution around the individual spots. Figure 6 shows three DLIT images and three EL images of a mc-Si solar cell for applied voltages ranging from Ϫ10 to Ϫ16 V. Comparing the two sets of images, we find a very good correlation between the reverse-EL and reverse-DLIT signal since the emission of light is always accompanied by a temperature increase.…”

Water Ingress in Encapsulated Inverted Organic Solar Cells: Correlating Infrared Imaging and Photovoltaic Performance

“…[ 46,47,[53][54][55] Recently, these techniques have been successfully applied to organic solar cells and modules in order to characterize macroscopic defects (e.g., electrode defects, shunts, etc. ), changes in sheet resistance, and for visualizing short circuit current distributions.…”